1. Field of the Invention
The present invention relates to plasma display panels and fabrication methods thereof, more particularly, to a method for fabrication of plasma display panel with high yield, improved reliability and reduced production cost, comprising low temperature firing process at not more than 300° C. to inhibit deformation of a substrate during processing, so as to fabricate large panels and simplify fabricating steps for the same and, in addition, a plasma display panel fabricated by the same.
2. Description of the Related Art
A plasma display panel generally has an upper plate and a lower plate combined together parallel to each other at constant interval, both of which play a role of displaying images.
There are a plurality of sustain electrodes arranged parallel to one another in the upper plate, each of which comprises a transparent electrode made of, for example, ITO (Indium Tin Oxide) and a bus electrode made of metal materials such as Ag arranged on the transparent electrode. Such sustain electrode is covered by a dielectric layer for restricting discharge current and insulating electrode pairs and further has a MgO deposited protective layer in order to improve discharge conditions over the dielectric layer.
Alternatively, the lower plate has barrier ribs arranged parallel to one another in form of stripes (or walls) to fabricate a number of discharge spaces called cells, as well as a plurality of address electrodes arranged parallel to the barrier ribs to implement address discharge at sites crossed with the sustain electrodes so as to emit vacuum ultraviolet (UV). Before fabricating the barrier ribs, a dielectric layer is formed on top of the address electrode by a firing process. Within the barrier ribs at top of the lower plate, a R.G.B fluorescence layer is applied to emit visible light for image displaying.
After sealing such fabricated upper and lower plates together using a sealing material, the discharge space is cleared of residual impurities through heat exhaustion and in return filled with gas to generate plasma, thereby completing production of the plasma display panel.
However, since conventionally known processes for fabrication of plasma display panels have often employed paste materials or a slurry type of glass frit as dielectric material, barrier rib material and/or sealing material, the processes require high firing temperature in the range of 500 to 600° C. to cure any of the above materials. In case of not using Pb as a representative softening material, the firing temperature must be raised. Such process with high temperature heat history has problems in that it causes alteration of glass dimension, pattern deviation leading to defect of display panels, and/or difficulties in enlargement of panel screen, and the like. Therefore, PDP substrates for supporting the barrier ribs must be made of special glass without softening at high temperature.
For a transparent dielectric substance for the plasma display panel, a glass paste for the dielectric substance comprises PbO—B2O3—SiO2 based glass powder containing excess of PbO, filler, organic solvent and polymer resin. In this case, the plasma display panel is fabricated by forming a thick film on a glass plate by a screen printing process and firing the laminate at high temperature of 500 to 600° C. In order to form a dielectric film with high light transmission properties in the plasma display panel, it is very important to eliminate foam contained in the dielectric film and it is necessary to control composition, particle diameter, production conditions and/or firing conditions of glass powder in detail.
Dielectric strength property of a dielectric substance in a plasma display panel is an essential element in driving the display panel and, if the substance is formed of glass paste, the dielectric strength is decreased due to foam generated according to sintering conditions and/or surface conditions of glass powder of the glass paste. Metallic Pb remaining in the dielectric film after firing reduces the dielectric strength of a dielectric layer and, in turn, decreases performance of the dielectric substance.
For a process for fabrication of plasma display panel using glass frit which mainly comprises low melting point glass, it is difficult to produce a transparent dielectric substance having low temperature firing properties without addition of excess Pb. Also, low melting point glass pastes need high firing temperature in the range of 550 to 580° C. A heat history process at more than 500° C. has drawbacks such as alteration of glass dimension, pattern distortion leading to defect of display panels, and/or difficulties in enlargement of panel screen.
In case of low melting point glass mainly comprising Pb ingredient, the glass generates high current during discharging to raise power output of an electric device. Pb is widely known as one of environmental pollutants and may cause increase of expenses for treatment of environmental pollution and wastes, especially, if large quantities of waste materials are generated, for example, during formation of barrier ribs in a lower plate of a plasma display panel.
Japanese Patent Laid-Open No. H9-199037 and H9-278482 disclosed Na2O—B2O3—SiO2 based glass with softening point of 500 to 600° C. and Na2O—B2O3—ZnO based glass free of Pb ingredient. Such glasses may further contain softening point lowering ingredients comprising alkali metal oxides such as sodium oxide Na2O, potassium oxide K2O, lithium oxide Li2O, etc. and may implement firing of a dielectric layer at relatively lower temperature. However, when a glass material containing the softening point lowering ingredients is used to prepare a dielectric layer, the glass material potentially causes yellowing of the dielectric layer or a front glass plate and has a relatively higher firing temperature of above 500° C., therefore, is restricted in application for typical substrates such as low price soda-lime glass substrates or thin metal substrates.
International Patent Application No. PCT-JP2002-006666 disclosed a method for yellowing reduction of Na2O—B2O3—SiO2 based glass and/or Na2O—B2O3—ZnO based glass and proposed zinc oxide, boron oxide, lithium oxide, sodium oxide, potassium oxide, rubidium oxide, cesium oxide, copper oxide, silver oxide, manganese oxide(IV), cerium oxide(IV), tin oxide(IV), antimony oxide(IV) and the like as constitutional ingredients of dielectric materials, all of which have firing temperatures of not less than 500° C.
Although formation of a dielectric layer using low melting point glass paste commonly adopts a screen printing process, this requires a very complicated process since the printing process is repeated two or more times to increase thickness of a film. Especially, as a barrier rib in a lower plate for a plasma display panel requires a thicker film than that of a dielectric layer, the barrier rib can be formed by repeating the printing process about eight (8) times. However, as a film fabricated using a glass paste has surface planarity altered depending on firing conditions, careful attention must be taken during the film fabrication process. In order to overcome shortcomings of the screen printing process, Japanese Patent Laid-Open No. H9-102273 disclosed a PDP fabrication process comprising the steps of: applying a glass paste composition to a supporting film to prepare a coating film; drying the coating film to form a film formation material layer; transferring the material layer formed on the supporting film to surface of a glass substrate on which electrodes are fixed; and firing the transferred material layer, thereby forming a dielectric layer on the surface of the glass substrate (that is, dry film formation process). However, although a lithographic process using a dry film can simplify processing steps of the PDP fabrication method, this adopts common low melting point glass pastes and still involves possible defects of dielectric material such as alteration of surface planarity depending on firing conditions.
International Patent Application No. PCT-JP2001-02289 and Korean Patent Application No. 2002-46902 suggested a dielectric composition and/or barrier rib composition which can be fired at relatively low temperature and comprises silicon resin and inorganic-organic combination, compared to typical low melting point glass containing Pb ingredients. Both of these patents proposed a variety of processes for fabrication of dielectric substances including such as spin coating, bar coating and/or painting process other than conventional printing process. In addition, these have advantages of excellent applicability in lithography using the dry film and reduction of dielectric strength caused by foam during the firing process. If silicon resin or inorganic-organic combination is contained in the dielectric composition, the dielectric composition can solve existing problems including environmental pollution caused by Pb ingredient, functional deterioration of dielectrics, high power consumption caused by high dielectric constant, minute dimensional deformation caused by high firing temperature, restriction of substrates and so on. In particular, a low temperature firing process enables low temperature substrates and/or thin substrates to be used, inhibits deformation of substrates to result in manufacturing of large panels and simplifies processes for fabrication of display panels, thereby accomplishing fabrication of low price PDPs with high yield and excellent reliability.
Barrier rib materials used in lower plates of plasma display panels are generally manufactured by adding white and black pigments to dielectric materials useful for front substrates of the display panels. Different processes for fabrication of barrier ribs in various forms have been proposed on the basis of compositions of the dielectric materials. For a 42-inch panel, a dielectric layer with height equal to overall height of a barrier rib is normally formed by a screen printing process and structure of the barrier rib is usually formed by a sandblasting process. In contrast, with regard to fabrication of HDTV grade of plasma display panels with dimension of more than 60-inch, the screen printing process through multi-printing or sandblasting process is not suitable for manufacturing complicated structures with precise dimensions because these panels need smaller pitch between structures and high flatness of structure. In order to solve problems in relation to complexity of such process caused by complicated multi-screen printing as well as formation of uniform barrier rib dielectric bodies, Japanese Patent Laid-Open Nos. H9-102273 and H9-101673 proposed formation of barrier rib layers in a single process using a transfer film (that is, a complex film which comprises a film formation material layer obtained from a glass paste composition and a supporting film, and a cover film easily detachably laminated on top of the material layer). But, this method also has drawbacks such as restriction of substrates made of low melting point fired glass, difficulties in formation of microfine patterns, surface planarity and/or generation of environmental wastes, although it can simplify fabrication processes.
Therefore, in order to produce high resolution plasma display panels with large screen area using low price substrates, there are still a requirement for development of a novel material that has large thickness and enables formation of microfine patterns, which is prepared in a single process, as well as a low temperature firing process of barrier rib.
For general fabrication of a plasma display panel, glass is used as a sealing material to combine and seal an outline of upper and lower plates of the panel after overlapping the upper and lower plates. During sealing the outline of the upper and lower plates, the sealing material must have firing point reduced as much as possible to protect characteristics of barrier ribs, fluorescence layers and/or dielectric layers which were already formed in the panel.
Glass based sealing compositions for plasma display panel conventionally known in the related art are mainly prepared from PbO—B2O3 or PbO—ZnO—B2O3 materials. Illustrative examples of the compositions include LS-0118, LS-0206, GA-0951, LS-7201, LS-7105, etc. having firing points in the range of 340 to 400° C., which are available from NEG, Japan.
However, since the above compositions contain PbO ingredients harmful to human body, these adversely affect ecosystems through environmental pollution and/or degradation of natural ecosystems during disposal of products containing the compositions.